As handsets and other wireless communication devices become smaller and embedded with more applications, new antenna designs are required to address inherent limitations of these devices. With classical antenna structures, a certain physical volume is required to produce a resonant antenna structure at a particular radio frequency and with a particular bandwidth. In multi-band applications, more than one such resonant antenna structure may be required. With the advent of a new generation of wireless devices, such classical antenna structure will need to cover wider bandwidths and maintain or increase efficiency across the entire frequency range.
IMD (Isolated Magnetic Dipole) technology has been developed over the past several years to provide superior efficiency, isolation, and selectivity characteristics from embedded antennas in small wireless devices. An IMD antenna is designed to excite a magnetic dipole mode from a metal structure in such a fashion as to minimize the fringing fields typically generated between an antenna element and an adjacent ground plane. A current is induced on the antenna structure and a strong electric field is generated on the structure in the plane of the IMD element instead of a strong fringing field to the ground plane. By minimizing the coupled fields to the ground plane, with the circuit board of a wireless device taking the place of the ground plane, improved efficiency and isolation can be obtained. Single and multi-resonant elements can be created to address a wide range of frequency bands.
This patent application involves the use of a second conductive element coupled to an antenna element to improve frequency bandwidth. Lumped components such as capacitors and inductors can be attached to either conductive element and used to increase the bandwidth or shift the frequency of operation. Active components can be used to dynamically tune the antenna. The present invention addresses the need to create more efficient antennas with a higher bandwidth adaptable to fit within present device designs.